1. Field of the Invention
The present invention relates to a method of manufacturing a preform for a connecting rod of an engine. The connecting rod has a large-end portion, a small-end portion, and a rod portion which lies between the large-end portion and the small-end portion. The preform is used as a raw material (or a blank) in forming the connecting rod by means of forging.
2. Description of Related Art
As a method of manufacturing a connecting rod of an engine, there has hitherto been known the following in Published Unexamined Japanese Patent Application No. 137640/1986. Namely, in the method, a preform having a shaft portion corresponding to the rod portion of the connecting rod, that large-end mass portion on one end of the shaft portion which corresponds to the large-end portion thereof, and that small-end mass portion on the opposite end of the shaft portion which corresponds to the small-end portion thereof is set inside a die of a forging die apparatus. The connecting rod is thus formed by forging. The preform is normally manufactured by swaging.
Forming by the process of swaging is sequentially performed while either a die or a blank is rotated. The preform for a connecting rod has a large difference in diameters between the large-end mass portion and the shaft portion. Therefore, there is a disadvantage in that the forming takes time and that the equipment becomes large in size.
In view of the above points, the present invention has an object of providing a method of manufacturing a preform for a connecting rod of an engine, in which the productivity can be improved.
In order to attain the above and other objects, the present invention is a method of manufacturing a preform for a connecting rod of an engine, the connecting rod having a large-end portion, a small-end portion, and a rod portion between the large-end portion and the small-end portion, the preform being used for forging the connecting rod and having a shaft portion corresponding to the rod portion, that large-end mass portion on one end of the shaft portion which corresponds to the large-end portion, and that small-end mass portion on the other end of the shaft portion which corresponds to the small-end portion, the method comprising the steps of: forming a preform blank comprising the large-end mass portion and a shaft-shaped portion, the shaft-shaped portion being formed by extrusion and including the shaft portion and an extended portion which extends axially forward from the shaft portion; and forming the small-end mass portion by squeezing the extended portion in the axial direction.
According to the present invention, the shaft portion which has a large difference in diameter relative to the large-end mass portion is formed by extrusion together with the extended potion which is converted into the small-end mass portion. Therefore, the forming of the shaft portion does not take much time and, therefore, the productivity of the preform is improved.
The upsetting ratio of the small-end mass portion (axial length of the extended portion required for forming the small-end mass portion/diameter of the extended portion) becomes relatively large. Therefore, at the time of squeezing, the extended portion is likely to give rise to buckling. Since buckling becomes the cause for poor forming such as the presence of biased material thicknesses, folds, or the like, it is preferable to prevent the occurrence of buckling. In this case, if the step of forming the small-end mass portion comprises squeezing the extended portion in a plurality of times starting with a portion near the shaft portion, the upsetting ratio per one time (length of squeezing of the extended portion/diameter of the extended portion) becomes small. As a result, the occurrence of buckling can be prevented, and the small-end mass portion can be formed at a higher accuracy.
The conventional large-end mass portion and the small-end mass portion are formed into a sphere or a circular column. This kind of preform is, however, poor in sitting stability. Therefore, the preform is likely to roll (or move) inside the die of the forging die apparatus out of an ordinary set position. Biased material thicknesses will thus occur due to this positional deviation, resulting in a poor forming accuracy of the connecting rod. As a solution, it is preferable in the step of forming the preform blank, the large-end mass portion is formed into a noncircular cross section having flat surfaces which are parallel with an axial line of the shaft portion, the flat surfaces being formed in a part along an outer periphery of the large-end mass portion. According to this arrangement, when the preform is set inside the die of the forging die apparatus, the flat surface of the large-end mass portion is caused to sit on the die surface. The preform is thus prevented from rolling inside the die. As a result, the biased material thicknesses due to the positional deviation of the preform can be prevented.